There are many situations where a regulation of the setting for a mortar or a concrete composition based on Portland cement and/or on calcium aluminate cement is expected. This is the case especially for the building or the repair of civil engineering works, such as street or road pavements, sidewalks. To be also mentioned are maintenance and construction of electric cable networks, pipe networks for gas and water distribution. Repair works for technical facilities often require underground cavities to be dug, which are sources of complications for the users of such facilities. Thus, it is essential for such cavities to be rapidly filled, so that said facilities can be put in service again as soon as possible after the end of the works.
During the recent years, the composition of cement-based systems has changed in favor of concrete formulations with a (very) high initial strength. However such high mechanical resistances often go along with a very fast initial setting (of about a couple of minutes), which makes this type of concrete casting with no additive difficult, or even impossible.
In order to slow down these setting times, set-controlling agents have been developed.
The patent application EP 0081385 discloses an aluminous cement, which setting is inhibited through a set inhibitor, for example boric acid. Aluminous cement setting is caused by the incorporation of a reactivator within the aluminous cement, for example lime, present in an amount ranging from 0.1 to 10% by weight as compared to the aluminous cement weight.
Also known from the state of the art is WO2004/060828, which describes a setting agent for a Portland cement-containing composition. This setting agent comes in an aqueous form and comprises calcium aluminate and, by weight, as compared to such calcium aluminate total weight, from 0.5 to 4% of a set inhibitor and an anti-settling agent. In particular, the set inhibitor of the calcium aluminate-based cement is chosen from boric acid, citric acid or one of their salts.
JP2007-297250 describes an ultra-fast setting cement composition comprising Portland cement, amorphous calcium aluminate with a CaO/Al2O3 molar ratio between 1.25 and 1.75, anhydrous calcium sulfate and a set-controlling agent (alkali metal aluminate and organic acid).
CN 102 765 738 describes an amorphous calcium aluminate composition, as well as the method for making the same. Amorphous calcium aluminate may be used as an additive for a cement-based composition, so as to improve its setting time or as an additive for steel production. In particular, amorphous calcium aluminate comprises, by weight, as compared to its total weight, from 40 to 60% of CaO (C), from 30 to 60% of Al2O3 (A), from 0.01 to 1% of S, from 1 to 10% of SiO2, from 0.05 to 3% of Fe2O3, from 0.01 to 5% of CaF2, from 1 to 10% of MgO, from 0 to 3% of TiO2 and from 0.01 to 1% of P.
JP 2007 297250 describes a cement composition containing Portland cement, amorphous calcium aluminate, anhydrous gypsum (calcium sulfate), alkali metal aluminate and additives (gas-entraining agent), as well as impurities. This document teaches that if the whole amount of impurities is lower than 10%, then these impurities do not affect the amorphous calcium aluminate properties.
KR 10200 7001 6170 describes a set accelerator comprising calcium aluminate (vitrification rate of 80% or higher), gypsum and an alkali metal aluminate.
Although the setting accelerators of the prior art are satisfying, there is still a need for new compositions enabling to regulate the setting of cement and in particular a cement based on amorphous calcium aluminate combined, or not, with Portland cement, which would also be able to preserve the mechanical properties of the thus obtained mortar or concrete.
It is thus an objective of the present invention to provide a new ultra-fast setting cement composition, which avoids, at least partially, the abovementioned drawbacks, and which especially enables to better regulate the setting of cement over time, as compared to the previously mentioned state of the art.